Bottom Line:
For the first time, the protective effect of α-tocopherol was shown to depend on its concentration in the nanomolar range (1 nM < 10 nM < 100 nM), if the pre-incubation time was 18 h.Nanomolar and micromolar α-tocopherol decreased the number of PC12 cells in late apoptosis induced by H(2)O(2) to the same extent if pre-incubation time was 18 h.The data obtained suggest that inhibition by α-tocopherol in late stage ERK 1/2 and Akt activation induced by H(2)O(2) in PC12 cells makes contribution to its protective effect, while total inhibition of these enzymes is not protective.

ABSTRACTThe aim of this work was to compare protective and anti-apoptotic effects of α-tocopherol at nanomolar and micromolar concentrations against 0.2 mM H(2)O(2)-induced toxicity in the PC12 neuronal cell line and to reveal protein kinases that contribute to α-tocopherol protective action. The protection by 100 nM α-tocopherol against H(2)O(2)-induced PC12 cell death was pronounced if the time of pre-incubation with α-tocopherol was 3-18 h. For the first time, the protective effect of α-tocopherol was shown to depend on its concentration in the nanomolar range (1 nM < 10 nM < 100 nM), if the pre-incubation time was 18 h. Nanomolar and micromolar α-tocopherol decreased the number of PC12 cells in late apoptosis induced by H(2)O(2) to the same extent if pre-incubation time was 18 h. Immunoblotting data showed that α-tocopherol markedly diminished the time of maximal activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and protein kinase B (Akt)-induced in PC12 cells by H(2)O(2). Inhibitors of MEK 1/2, PI 3-kinase and protein kinase C (PKC) diminished the protective effect of α-tocopherol against H(2)O(2)-initiated toxicity if the pre-incubation time was long. The modulation of ERK 1/2, Akt and PKC activities appears to participate in the protection by α-tocopherol against H(2)O(2)-induced death of PC12 cells. The data obtained suggest that inhibition by α-tocopherol in late stage ERK 1/2 and Akt activation induced by H(2)O(2) in PC12 cells makes contribution to its protective effect, while total inhibition of these enzymes is not protective.

f1-ijms-13-11543: The figure shows that α-T at concentrations of 100 nM, 1 μM, 10 μM or 100 μM has a pronounced cytoprotective effect on the viability of PC12 cells if pre-incubation with α-T is performed for 18 h prior to exposure of the cells to 0.2 mM H2O2 for 24 h. No significant difference is revealed in the effect of α-T in these concentrations. The effect of 10 nM α-T is lower than the effect of all higher concentrations of this compound tested, but it is significant. In this figure, the results of one typical experiment (from five replicates) are presented as means ± SEM of 2–3 parallel determinations. The differences are significant by one-way ANOVA followed by Tukey’s multiple comparison test: * as compared to control values, p < 0.01; x as compared to the effect of H2O2 alone, p < 0.05; # as compared to the effect of α-T at all higher concentrations, p < 0.01.

Mentions:
If pre-incubation with α-T was performed for 18 h (n = 5) the rescue rates of 100 nM, 1 μM, 10 μM and 100 μM α-T against H2O2-induced cell death were found to be 48.3% ± 5.7%, 48.2% ± 7.8%, 47.1% ± 5.8% and 57.7% ± 4.2%, respectively (the difference between these values is not significant: p > 0.05 in all cases). Thus, the similar protection of PC12 cells against H2O2-induced death was achieved by long pre-incubation with α-T in the range from 100 nM to 100 μM. At a concentration of 10 nM, α-T still significantly inhibited the toxic effect of H2O2 by 29.6% ± 3.6% (p < 0.01), albeit to a lower extent than α-T at the higher concentrations tested (p < 0.02). The results of a typical experiment are shown in Figure 1.

f1-ijms-13-11543: The figure shows that α-T at concentrations of 100 nM, 1 μM, 10 μM or 100 μM has a pronounced cytoprotective effect on the viability of PC12 cells if pre-incubation with α-T is performed for 18 h prior to exposure of the cells to 0.2 mM H2O2 for 24 h. No significant difference is revealed in the effect of α-T in these concentrations. The effect of 10 nM α-T is lower than the effect of all higher concentrations of this compound tested, but it is significant. In this figure, the results of one typical experiment (from five replicates) are presented as means ± SEM of 2–3 parallel determinations. The differences are significant by one-way ANOVA followed by Tukey’s multiple comparison test: * as compared to control values, p < 0.01; x as compared to the effect of H2O2 alone, p < 0.05; # as compared to the effect of α-T at all higher concentrations, p < 0.01.

Mentions:
If pre-incubation with α-T was performed for 18 h (n = 5) the rescue rates of 100 nM, 1 μM, 10 μM and 100 μM α-T against H2O2-induced cell death were found to be 48.3% ± 5.7%, 48.2% ± 7.8%, 47.1% ± 5.8% and 57.7% ± 4.2%, respectively (the difference between these values is not significant: p > 0.05 in all cases). Thus, the similar protection of PC12 cells against H2O2-induced death was achieved by long pre-incubation with α-T in the range from 100 nM to 100 μM. At a concentration of 10 nM, α-T still significantly inhibited the toxic effect of H2O2 by 29.6% ± 3.6% (p < 0.01), albeit to a lower extent than α-T at the higher concentrations tested (p < 0.02). The results of a typical experiment are shown in Figure 1.

Bottom Line:
For the first time, the protective effect of α-tocopherol was shown to depend on its concentration in the nanomolar range (1 nM < 10 nM < 100 nM), if the pre-incubation time was 18 h.Nanomolar and micromolar α-tocopherol decreased the number of PC12 cells in late apoptosis induced by H(2)O(2) to the same extent if pre-incubation time was 18 h.The data obtained suggest that inhibition by α-tocopherol in late stage ERK 1/2 and Akt activation induced by H(2)O(2) in PC12 cells makes contribution to its protective effect, while total inhibition of these enzymes is not protective.

ABSTRACTThe aim of this work was to compare protective and anti-apoptotic effects of α-tocopherol at nanomolar and micromolar concentrations against 0.2 mM H(2)O(2)-induced toxicity in the PC12 neuronal cell line and to reveal protein kinases that contribute to α-tocopherol protective action. The protection by 100 nM α-tocopherol against H(2)O(2)-induced PC12 cell death was pronounced if the time of pre-incubation with α-tocopherol was 3-18 h. For the first time, the protective effect of α-tocopherol was shown to depend on its concentration in the nanomolar range (1 nM < 10 nM < 100 nM), if the pre-incubation time was 18 h. Nanomolar and micromolar α-tocopherol decreased the number of PC12 cells in late apoptosis induced by H(2)O(2) to the same extent if pre-incubation time was 18 h. Immunoblotting data showed that α-tocopherol markedly diminished the time of maximal activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and protein kinase B (Akt)-induced in PC12 cells by H(2)O(2). Inhibitors of MEK 1/2, PI 3-kinase and protein kinase C (PKC) diminished the protective effect of α-tocopherol against H(2)O(2)-initiated toxicity if the pre-incubation time was long. The modulation of ERK 1/2, Akt and PKC activities appears to participate in the protection by α-tocopherol against H(2)O(2)-induced death of PC12 cells. The data obtained suggest that inhibition by α-tocopherol in late stage ERK 1/2 and Akt activation induced by H(2)O(2) in PC12 cells makes contribution to its protective effect, while total inhibition of these enzymes is not protective.